1. Field of the Invention
The present invention relates to an apparatus and a method for writing and reading digital information on a magnetic memory.
2. Description of the Prior Art
Magnetic memories using as storage mediums magnetic tapes, magnetic disks and the like have been utilized in external memories for main computers. In such a memory, a magnetic-field detector, called a magnetic head, is provided in proximately contact with the magnetic storage medium in order to detect the magnetic fields induced by respective very small storage domains thereof. The most problematic shortcoming of such a conventional structure is that the head has to make contact with the storage medium so that it is very difficult to improve the reproducing speed and to lengthen the life time of the storage medium. The memory capacities have also been limited due to the area picked up by the head.
Recently, optical disks have been developed in which a laser beam focussed in a very tiny area is directed to depressions formed on the surface of a disk in order to read out information represented by the depressions. The above-mentioned problems have been greatly improved in such optical disks. On the other hand, there has not yet been developed an optical disk which can be repeatedly rewritten. Some researchers have carried out their efforts to utilize opto-magnetic effects such as Faraday effect in order to make rewritable disks. In spite of such efforts, however, there has been not proposed so far practical devices.
The advantage of the use of magnetic phenomena for information storage is the simple process of recording and the stability of stored information for a long time. However, the reproducing of information recorded on an opto-magnetic disk, as described above, is very difficult. On the other hand, the reproducing by means of a head making in contact with the storage medium can be carried out easily whereas there are in this case many shortcomings as described above.
One of solutions of these problems is the use of light rays or electron beams by which read-write operation is carried out. It is, however, impossible to detect a static magnetic field by light rays alone because electromagnetic waves shall not interact with static fields.
In accordance with the mechanism of opto-magnetic storage currently proposed, a magnetic flux is detected in terms of indirect interaction between the flux and photons through a certain mediating substance. The interaction, however, is very weak and therefore leaving various technical problems.
On the other hand, it is possible to detect existence of magnetic fluxes through interaction between a magnetic field and a spin angular momentum. The electric interaction of electrons having 1/2 spin quantum number, however, is substantially stronger than the magnetic interaction thereof, and therefore it is in practice impossible to magnetically detect by such interaction. Neutrons shall not electrically interact with substances so that it is theoretically possible to read out magnetically recorded information. It is, however, not practical.